Molecular analysis of the Huntington's disease gene in New Zealand

Abstract

Aims: To establish and validate a polymerase chain reaction (PCR)-based diagnostic test in New Zealand, which enables the number of CAG repeats present in the Huntington's disease (HD) gene to be determined with speed and accuracy. To develop procedures for reporting and counselling probands and families.

Methods: The analysis of the CAG repeat region in Huntington's disease and normal chromosomes involved PCR amplification of genomic DNA using either the incorporation of radioactive deoxynucleotides or fluorescent oligonucleotide primers.

Results: The molecular analysis of the CAG repeat sequence in the Huntington's disease gene of over 100 New Zealand individuals has been performed. Huntington's disease chromosomes contained 37-70 (median 44) repeats whereas normal chromosomes contained 9-27 (median 18) repeats. Six individuals from three families had an allele in the intermediate range (30-36 repeats). Instability of the CAG repeat upon transmission from generation to generation was also observed. A comparison of the results obtained using radioactive and fluorescent assays indicates that while both methods are reliable, the latter method is more rapid and allows for automation to be incorporated in the scoring of allele sizes.

Conclusions: Our analysis of Huntington's disease alleles has shown a profile of CAG repeat lengths that is consistent with those reported internationally. In addition, reporting and counselling procedures have been established for presymptomatic testing of Huntington's disease in New Zealand.